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  <title></title>
  <style type="text/css">
    /* * {
      margin: 0;
      padding: 0;
    }
    ul {
      list-style: none;
    }
    .wrap {
      width: 330px;
      height: 30px;
      margin: 100px auto 0;
      padding-left: 10px;
      background-color: skyblue;
    }
    .wrap li {
      background-color: skyblue;
    }
    .wrap > ul > li {
      float: left;
      margin-right: 10px;
      position: relative;
    }
    .wrap a {
      display: block;
      height: 30px;
      width: 100px;
      text-decoration: none;
      color: #000;
      line-height: 30px;
      text-align: center;
    }
    .wrap li ul {
      position: absolute;
      top: 30px;
      display: none;
    } */
  </style>
  <script src="jquery-2.0.0.min.js"></script>
  <script>
    $(function () {
      //获取所有li，添加移入事件
      $(".wrap>ul>li").mouseenter(function () {
        //设置内部的子元素ul slideDown
        $(this).children("ul").stop().show(600);
      });
      //移出li时，让内部子元素slideUp
      $(".wrap>ul>li").mouseleave(function () {
        $(this).children("ul").stop().hide(600);
      });
      //如果当前运动没有完毕，又添加了新的动画，这时新的动画需要等待当前动画执行完毕才会开始
      //如果持续添加。一定会造成动画的积累，这种情况我们称为动画队列
    });
  </script>
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      <a href="javascript:void(0);" rel="external nofollow" >一级菜单1</a>
      <ul class="ul">
        <li>二级菜单11</li>
        <li>二级菜单12</li>
        <li>二级菜单13</li>
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      <a href="javascript:void(0);"  >一级菜单2</a>
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        <li><a href="javascript:void(0);"  rel="external nofollow" >二级菜单21</a></li>
        <li><a href="javascript:void(0);"  rel="external nofollow" >二级菜单22</a></li>
        <li><a href="javascript:void(0);"  rel="external nofollow" >二级菜单23</a></li>
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      <a href="javascript:void(0);"  rel="external nofollow" >一级菜单3</a>
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        <li><a href="javascript:void(0);"  rel="external nofollow" >二级菜单31</a></li>
        <li><a href="javascript:void(0);"  rel="external nofollow" >二级菜单32</a></li>
        <li><a href="javascript:void(0);"  rel="external nofollow" >二级菜单33</a></li>
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